Thermally insulated die plate assembly for underwater pelletizing and the like

ABSTRACT

An insulated die plate assembly for use in underwater pelletizing and other granulation processes includes a thin, continuous air chamber formed across the plate assembly generally parallel to the die face such that the heated upstream portion of the die plate assembly is thermally insulated from the downstream portion. The air chamber is atmospherically equilibrated by venting the air chamber to the atmosphere. The plurality of extrusion orifices, either individually or in groups, are formed in extrusion orifice extensions that extend through the insulation chamber so that the process melt to be granulated can pass therethrough. The orifice extensions and the components forming the air chamber around the orifice extensions channel heat along said extensions to maintain the process melt therein at a desired temperature, to help rigidify the die plate assembly and to better seal the air chamber.

This application is a continuation application of Ser. No. 13/353,030,filed Jan. 18, 2012, which was a continuation application of Ser. No.12/222,669, filed Aug. 13, 2008, and hereby claims the priority thereofto which it is entitled.

FIELD OF THE INVENTION

The present invention generally relates to an insulated die plateassembly for use in underwater pelletizers and other granulationprocesses that include hot-face or non-fluidic pelletization. Morespecifically, the present invention relates to an insulated die plateassembly that includes a thin continuous air pocket or chamber formedacross the plate assembly such that the upstream portion of the dieplate assembly is thermally insulated from the downstream portion of thesame assembly, thus allowing the respective portions to co-exist atdifferent temperatures. The plurality of extrusion orifices,individually or in groups, extend through extrusion orifice extensionsthat project through the insulation air pocket or chamber so that thematerial to be pelletized or granulated can pass therethrough.

BACKGROUND OF THE INVENTION AND PRIOR ART

Underwater pelletization equipment and its use following extrusionprocessing have been implemented for many years by Gala Industries, Inc.(“Gala”), the assignee of the present invention. Pelletization dies anddie plates, in particular, are demonstrated in prior art disclosuresincluding, for example, U.S. Pat. Nos. 4,123,207, 4,500,271, 4,621,996,4,728,276, 5,059,103, 5,403,176, 6,824,371, 7,033,152, U.S. PatentApplication Publication Nos. 20060165834 and 20070254059, German Patentsand Applications including DE 32 43 332, DE 37 02 841, DE 87 01 490, DE196 51 354, and World Patent Application Publications WO2006/081140 andWO2006/087179. These patents and applications are all owned by Gala andare expressly incorporated herein by reference as if set forth in theirentirety.

As well understood by those skilled in the art, die plates used withrotating cutter hubs and blades, such as in underwater pelletizing, havethe extrusion orifices or through die holes arranged in a generallycircular pattern, or groups of multiple die holes arranged (as in podsor clusters) in a generally circular array. As so arranged, the rotatingblades can cut the extrudate as it exits the die holes along a circularcutting face.

It is known in the field of plastic extrusion and cutting to feedplastic into a die plate for extrusion and solidification upon the exitfrom the die plate, and then to cut the extruded plastic into smallpieces externally of the die plate. However, a known problem consists ofthe plastic freezing up within the die holes and either partially orcompletely blocking the passage of the plastic therethrough, with theresulting disruption of the entire operation.

To maintain the polymer at a sufficiently high temperature, insulationis desirable to reduce heat transfer from the extrusion die and themolten polymer being extruded through the extrusion orifices to thewater circulating through the water box of the underwater pelletizer.Ineffective insulation can result in excessive cooling of the moltenpolymer as it is being extruded through the extrusion orifices causingfreeze off of the molten polymer at the die face.

U.S. Pat. No. 4,378,964 and World Patent Application Publication No.WO1981/001980 disclose a multi-layer die plate assembly for underwaterpelletization of polymeric materials in which an insulation layer,preferably zirconium oxide, is fixedly positioned between the body ofthe die plate and the layers comprising the cutting face of the die.Adjacent or proximal to the insulation layer is a heating chamberthrough which is circulated a heating fluid for maintenance of thetemperature of the die.

U.S. Pat. No. 4,764,100 discloses a die plate construction specificallydescribed for underwater pelletization of plastic extrudate including aclosed insulating space formed between the baseplate and the cuttingplate through which penetrates the extrusion nozzles, and optionalinserts serve to further strengthen and support the structure.

Vacuum heat insulating cavities between extrusion nozzles are disclosedin U.S. Pat. No. 5,714,713 in a multi-step process that includeselectron beam welding while the die components are maintained under highvacuum. This disclosure is extended to vacuum heat insulation portionsin areas peripherally external to the extrusion nozzles for enhancedinsulation performance in U.S. Pat. No. 5,989,009.

Similarly, closed continuous thermal stabilization cavities filled withair or gas are disclosed in U.S. Pat. No. 6,976,834. Additionally,brazing in a furnace at high temperature, 900° C. to 1200° C., undervacuum is disclosed as a manufacturing process with controlled coolingunder argon to prevent oxidation thusly presenting an opportunity tointroduce vacuum into the thermal stabilization cavities.

German Patent Application No. DE 100 02 408 and German Patent UtilityModel No. DE 200 05 026 disclose a hollow space or a multiplicitythereof in the inner region of the nozzle plate and the noseconeextension to enhance temperature control by virtue of the reduction ofmass necessitating temperature maintenance and thusly introducingthermal insulation. Use of solid, liquid, or gas as insulating materialsis disclosed therein.

World Patent Application Publication No. WO2003/031132 discloses the useof ceramic plates for insulation of the die face from the heated portionof the die body.

Finally, Austrian patent application AT 503 368 A1 discloses a thermallyinsulated die plate assembly with a detachable face plate that is sealedto the discharge end of the extrusion orifice nozzles by an O-ring ormetal seal. This die plate assembly is very fragile and highlysusceptible to process melt leakage, thus requiring considerablemaintenance.

There is, therefore, a need for a thermally insulated die plate assemblywhich is robust in construction, retains the air pocket in a sealedcondition, requires low maintenance and provides high performance.

SUMMARY OF THE INVENTION

The thermally insulated die plate assembly of the present invention isinstalled in a conventional manner between the melting and/or mixingdevices and the pellet transport components including mechanical,pneumatic, and/or fluid conveyance. The upstream side of the insulateddie plate assembly receives molten polymer or other fluidized materialfrom the melting/mixing devices that is subsequently extruded throughthe multiplicity of orifices extending from the upstream side to thedownstream side of the die plate assembly to form extruded strands ofmaterial. The extruded strands, with at least marginal cooling, are cutinto pellets by rotating cutter blades engaging a cutting surface orcutting die face associated with the downstream side of the die plate ina manner well known in the art of pelletizing.

The thermally insulated die plate assembly of the present invention isretained in position in a conventional manner by fasteners that connectthe melting and mixing components, the die plate, and the pellettransport components. The nose cone, optionally a separate component, isretained in position as required by the normally provided nose coneanchor bolt as is understood by those skilled in the art. Similarly,thermal regulation fluid as required enters and exits chambers in thedie plate through conventional inlet and outlet orifices, respectively.

The thermally insulated die plate assembly in accordance with thepresent invention is essentially formed by machining a cutout in thedownstream side or die face side of a die plate body, preferably forminga generally circular cavity. The periphery of the cutout cavity shouldextend beyond the circular pattern or array of extrusion orifices or dieholes with a raised circular ridge which matches and encompasses thecircular pattern or array of extrusion orifices or die holes. The raisedcircular ridge thus divides the cutout cavity into, preferably, anannular outer section and a circular inner section. The raised circularridge is preferably trapezoidal in vertical cross-section with theextrusion orifices extending centrally therethrough. Orifice protrusionsproject from the upper surface of the raised ridge at the extrusionorifice locations so that the extrusion orifices extend through theorifice protrusions.

Finally, a cover plate with holes matching the orifice protrusions issized to fit over and into the cutout cavity in the die plate body tocomplete the downstream side of the die plate assembly and form agenerally planar die face. In addition, the upstream side of the coverplate is machined with a counterbore which conforms to the configurationof the orifice protrusions and defines the outside wall of the aircavity around the orifice protrusions and the raised circular ridge. Thecover plate is attached around its periphery to the die plate body andattached around its matching holes to the distal end of the orificeprotrusions adjacent the die face.

The thickness of the cover plate is less than the depth of the cutoutcavity so that when the cover plate is in place a thin, generally flat,continuous air pocket or air chamber is formed around the raisedcircular ridge and associated orifice protrusions, which air chamber isgenerally parallel to the die face. The thickness of the air chamber ison the order of about 0.05 millimeters (mm) to about 6.0 mm, andpreferably about 0.5 mm to about 1.0 mm. Stated another way, thethickness of the air chamber is preferably about 5% to about 10% of thethickness of the die plate assembly.

The raised circular ridge and associated orifice protrusions whichencompass and extend the extrusion orifices from the base of the cutoutcavity to the matching holes of the cover plate are together referred toherein as the “extrusion orifice extensions”. The extrusion orificeextensions for each of the extrusion orifices or die holes extend fullythrough the air chamber so that the orifice extensions are surrounded bythe thermally insulating air.

The air chamber is preferably vented to the atmosphere outside the dieplate assembly, such as through one or more channels in the die platebody to provide for atmospheric equilibrium of the air chamber. The airchamber thus forms a thermally insulating air pocket or chamber betweenthe typically heated upstream side of the die plate assembly and thedownstream side forming the die face, which contacts the cooling waterof the waterbox in an underwater pelletizer, or other cooling mediumassociated with a rotating cutter hub and blade assembly.

The cover plate should be made of a chemical, corrosion, abrasion, andwear-resistant metal. The cover plate can contain at least onecircumferential expansion groove on at least one face and preferablycontains a multiplicity of circumferential expansion grooves on at leastone face. When expansion grooves are formed on both faces, they arepreferably arranged in a staggeringly alternating configuration.

Preferably, the cover plate is welded in position with nickel steel.More preferably, the cover plate is attached by welding with nickelsteel at peripheral grooves circumferentially surrounding the coverplate and at weld locations between the distal end of the orificeprotrusions and the inside of the cover plate holes.

The die plate body of the thermally insulated die plate assemblyaccording to the present invention can be thermally regulated by anysuitable heating system known to those skilled in the art, such asthermal regulation fluid as required to enter and exit heating chambersin the die plate body to conventional inlet and outlet orifices,respectively. Alternatively, the die plate body can be thermallyregulated by at least one of electrical resistance, induction, steam,and thermal transfer fluid. Preferably, the die plate body is heated byelectric heaters in techniques known to those skilled in the art.

In a first embodiment of the present invention, the thermally insulateddie plate assembly is configured with a one-piece die plate body. In asecond embodiment of the present invention, the thermally insulated dieplate assembly is configured with a two-piece die plate body having aremovable center die insert thermally insulated in accordance with thepresent invention which is peripherally surrounded by a die plate outerring thermally regulated by at least one of electrical resistance,induction, steam, and thermal transfer fluid.

As used herein the term “die plate body” is intended to include the bodyof the die plate when the assembly of the present invention isconfigured as a one-piece construction and the removable center dieinsert in combination with the die plate outer ring when the assembly isconfigured in a two-piece construction.

In addition to having the die face of uniform planarity, the annularcutting face containing the distal ends of the orifice protrusions, andthrough which penetrate the multiplicity of extrusion orifices, can beraised a certain distance above the remaining portion of the die face,as known to those skilled in the art. The rotating cutting blades thusengage the raised annular cutting face. The raised annular cutting faceshould be at least 0.025 millimeters higher than the surrounding dieface and preferably is at least 0.50 millimeters above the surroundingdie face.

Preferably, at least the surface of the annular cutting face engaged bythe cutting blades is subjected to an enhancing surface treatment. Theenhancing surface treatment includes at least one of nitriding,carbonitriding, electroplating, electroless plating, electroless nickeldispersion treatments, flame spraying including high velocityapplications, thermal spraying, plasma treatment, electrolytic plasmatreatments, sintering, powder coating, vacuum deposition, chemical vapordeposition, physical vapor deposition, sputtering techniques and spraycoating. These surface treatments result in metallizing, attachment ofmetal nitride, metal carbides, metal carbonitrides, and diamond-likecarbon and can be used singly and in any combination. Different surfacetreatments can be applied to different circumferential planes on thecutting face and should be at least approximately 0.025 millimeters inthickness. Preferably, the treatments are at least approximately 0.50millimeters in thickness.

The raised circular ridge and associated orifice protrusions are formedin at least one annular ring, and each orifice protrusion can contain atleast one to a multiplicity of extrusion orifices arranged in groups,pods, and clusters. The orifice protrusions can be of any geometryincluding at least one of oval, round, square, triangular, rectangular,polygonal, and in many combinations. Similarly, the orifice protrusionscan be arranged concentrically, alternating, in a staggeringconfiguration, and linearly, and can be positioned parallel to the arcof rotation of the cutting blades, perpendicular to the arc andincluding kidney to comma-like configurations.

In addition, the extrusion orifices can be of any geometry including butnot limited to round, oval, square, rectangular, triangular, pentagonal,hexagonal, polygonal, slotted, radially slotted and any combinationthereof. A multiplicity of extrusion orifices can be of differentgeometry in a particular orifice protrusion or die face.

In view of the foregoing, it is an object of the present invention toprovide a die plate assembly in which the typically heated upstreamportion of the assembly is thermally insulated from the typically cooleddownstream portion adjacent the die face by an internal insulation airpocket or air chamber extending substantially parallel to the die face.

A further object of the present invention is to provide a thermallyinsulated die plate assembly in accordance with the preceding object inwhich the insulation air pocket or air chamber surrounds extrusionorifice extensions configured as a raised circular ridge and associatedorifice protrusions, through which the extrusion orifices extend to thedie face.

Another object of the present invention is to provide a thermallyinsulated die plate assembly in accordance with the preceding object inwhich the insulation air pocket or air chamber is formed by machining orcutting out a cavity in the downstream side of a die plate body leavingin place the raised circular ridge. The cavity is closed by a coverplate having a counterbore sized to match the extrusion orificeextensions and with holes to match the distal ends of the orificeprotrusions.

Still another object of the present invention is to provide a thermallyinsulated die plate assembly in accordance with the two precedingobjects in which the raised ridge has a trapezoidal shape in verticalcross-section to aid in channeling heat to the orifice protrusions andthus maintain the process melt at a desired temperature in the extrusionorifice at the die face.

A still further object of the present invention is to provide athermally insulated die plate assembly in accordance with the precedingthree objects in which the insulation air pocket or air chamber isconfigured to follow and surround the raised circular ridge andassociated orifice protrusions so as to retain the heat in the raisedridge and orifice protrusions in order to maintain the process melt at adesired temperature in the extrusion orifices at the die face.

It is another object of the present invention to provide a thermallyinsulated die plate assembly in accordance with the preceding objects inwhich the insulation air pocket or air chamber is vented to theatmosphere outside of the die plate assembly to maintain the temperatureand pressure conditions inside the cavity or chamber equilibrated to theatmosphere.

It is a further object of the present invention to provide a thermallyinsulated die plate assembly in accordance with the preceding objects inwhich the die plate body is configured in a single-body construction.

Yet another object of the present invention is to provide a thermallyinsulated die plate assembly in accordance with the preceding objects inwhich the die plate body is configured in a two-piece constructionincluding a removable center die insert surrounded by a die plate outerring.

Still yet a further object of the present invention is to provide athermally insulated die plate assembly in accordance with the precedingobject in which the removable insert and the die plate outer ring can beindividually and/or separately heated or thermally regulated.

A final object to be set forth herein is to provide a thermallyinsulated die plate assembly which will conform to conventional forms ofmanufacture, will have improved strength and robustness, will maintainthe insulating air pocket tightly sealed to provide improved thermalinsulation in operation, and will be economically feasible, long-lastingand relatively trouble-free in use.

These together with other objects and advantages which will becomesubsequently apparent reside in the details of construction andoperation as more fully hereinafter described and claimed, referencebeing had to the accompanying drawings forming a part hereof, whereinlike numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical sectional view of a first embodiment of athermally insulated die plate assembly in accordance with the presentinvention in which the assembly is of a single body construction.

FIG. 2 is an enlarged schematic vertical sectional view illustratingfurther details of the components around an upper extrusion orifice forthe embodiment shown in FIG. 1.

FIG. 3 is a partial cut-away perspective view of the die plate assemblyshown in FIG. 1, illustrating the association of the various components.

FIG. 4 is a schematic vertical sectional view of a second embodiment ofa thermally insulated die plate assembly in accordance with the presentinvention in which the assembly is of a two-piece construction,including a removable center die insert and die plate outer ring.

FIG. 5 is a schematic vertical cut-away side perspective view ofone-half of the removable center insert of the die plate assembly shownin FIG. 4.

FIG. 6 is an enlarged view of the components shown in FIG. 5,illustrating the detail of the air chamber around the raised circularridge and the orifice protrusion.

FIG. 7 is a schematic top perspective view of one-half of the removablecenter insert of the die assembly shown in FIG. 4, showing the design ofthe raised circular ridge and the orifice protrusions associatedtherewith.

FIG. 8 is a schematic bottom perspective view of a cover plate which,when turned over, is assembled onto the top of the removable centerinsert shown in FIG. 7 to form the air pocket or air chamber of the dieplate assembly shown in FIG. 4.

FIG. 9 is an enlarged schematic vertical section view showing the coverplate of FIG. 8 assembled onto the removable insert shown in FIG. 7 withthe welds in place around the periphery of the cover plate and aroundthe extrusion orifices, together with a hard face on the downstreamsurface of the cover plate.

FIG. 10 is an exploded schematic vertical section view of a thermallyinsulated die plate assembly similar to FIG. 4 in which the removablecenter insert includes a separate center heating coil.

FIGS. 11 a-g are a composite perspective view illustrating variousconfigurations for the heat conducting protrusions in accordance withthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although only preferred embodiments of the invention are explained indetail it is to be understood that the invention is not limited in itsscope to the details of construction and arrangement of components setforth in the following description or illustrated in the drawings. Theinvention is capable of other embodiments and of being practiced orcarried out in various ways. Also, in describing the preferredembodiments, specific terminology will be resorted to for the sake ofclarity. It is to be understood that each specific term includes alltechnical equivalents which operate in a similar manner to accomplish asimilar purpose.

Referring to the drawings, FIGS. 1, 2 and 3 illustrate one embodiment ofthe present invention associated with components of a pelletizer, suchas an underwater pelletizer. The pelletizer includes an inlet housing 12from a melting and/or mixing apparatus (not shown). The inlet housing 12includes a passageway 14 for molten material or other extrudate(hereinafter collectively referred to as “process melt”) that caninclude organic materials, oligomers, polymers, waxes, and combinationsthereof without intending to be limited. Nose cone 16 directs theprocess melt to the upstream side of the single-body or one-piece dieplate assembly constructed in accordance with the present invention andgenerally designated by reference numeral 10. The nose cone 16 can beattachedly connected to the die plate assembly by a threaded rod (notshown). The threaded rod is screw threaded at one end into threaded bore18 of nose cone 16 and at its distal end into threaded bore 20 of dieplate 10. Alternately, the nose cone 16 can be rigidly affixed to orunitary with the die plate 10 and need not be attachedly connected asherein described.

The single-body die plate assembly 10 contains a multiplicity ofextrusion orifices 22 concentrically arranged singly or in multiplesthereof in at least one annular ring that extends from the upstream face24 to the downstream face or die face 26 of the die plate assembly 10. Aplurality of cutter blades 28 mounted on a rotatably driven cutter hub30 in a cutting chamber (not shown) cut the extruded and at leastpartially solidified process melt extruded through orifices 22 intopellets at the cutting surface of the die face 26. The pellets thuslyformed are transported mechanically, pneumatically, hydraulically, or incombinations thereof to downstream processing, such as a dewateringsystem, drying equipment and the like.

The die plate assembly 10 is made up with two major components, dieplate body 36 and cover plate 38. A thin, continuous air pocket or airchamber 32, parallel to die face 26, is formed between the downstreamside of the die plate body 36 and the upstream side of the cover plate38. In order for the extrusion orifices 22 to pass through the airchamber 32, the extrusion orifices 22 extend through a raised circularridge 34 formed in the downstream face of the die plate body and orificeprotrusions 35 positioned on top of the ridge 34 (see FIG. 2), whichtogether define the extrusion orifice extensions, generally designatedby reference numeral 31.

The upstream side of the cover plate 38 is provided with a generallycircular counterbore 76 which conforms to and receives the circulararray of orifice protrusions 35. The counterbore 76 has outlet holes 39which match the orifice protrusions 35 and form the distal ends 68 ofthe extrusion orifices 22. The distal ends 70 of protrusions 35 then fitinto the matching holes 39 in the cover plate 38. The raised circularridge 34 and associated heat conducting protrusions 35, which encompassand provide heat to the distal end 68 of the extrusion orifices 22, thusextend through and are surrounded by the air chamber 32.

In order to form the air pocket or air chamber 32, the central area ofthe downstream face 26 of die plate body 36 is machined or cut out toprovide a circular recess or cavity 33. The cavity 33 extends beyond theextrusion orifices 22 and is preferably formed with the raised circularridge 34 in place, although the ridge could be formed as a separatepiece and welded or otherwise attached to the bottom of the cavity 33.The raised ridge thus divides the cavity 33 into an annular outersection 72 and an inner circular section 74. The orifice protrusions 35can also be formed during the machining process and thus be integralwith the raised ridge 34. However, preferably, the protrusions 35 areconfigured as separate collars of the same material as the die platebody 36 (and ridge 34) and are adhered to the top of ridge 34 as bywelding or the like.

Circular cover plate 38 with holes 39 matching the distal ends 70 of theorifice protrusions 35 overlays the recess cavity 33 and is attachedlyconnected to die plate body 36 and to orifice protrusions 34 by brazing,welding, or similar technique known to those skilled in the art.Preferably, the cover plate 38 is constructed of an abrasion andcorrosion resistant metal and, more preferably, is constructed of nickelsteel. Similarly, attachment of the cover plate 38 to the die plate body36 and to the distal ends 70 of orifice protrusions 35 is preferablyachieved by welding and, more preferably, is achieved by nickel steelwelding. Weldments 40 and 42 are preferentially made at circumferentialgrooves 77 peripherally about the cover plate 38 and into the coverplate holes 39 which are sized to expose a portion of the distal end 70of protrusions 35 for welding or the like. To assist in rigidifying thecover plate 38 to the die plate body 36, the peripheral edge 80 isdesigned to rest on ledge 82 cut into the downstream face of the dieplate body. The peripheral edge 80 and the die plate body 36 haveopposing chamfers which form groove 77 for receiving the peripheral weld40 and maintain the peripheral edge 80 solidly against the ledge 82.

The surface of the cover plate 38 and thus the downstream face 26 ispreferably coated with a chemical, abrasion, corrosion, and wearresistant coating 60 as described hereinbelow. Once weldment 42 is inplace, along with wear resistant coating 60, if included, the distal end68 of the extrusion orifices 22 can be completed by machining from thedownstream side of the die plate assembly, such as with an EDM machineor otherwise as known by those skilled in the art, thus clearing anyweld 42 and coating 60 from the extrusion orifice distal end 68.

The raised circular ridge 34 is preferably trapezoidal in verticalcross-section to aid in channeling heat to the orifice protrusions 35,which transfer the heat from the raised ridge to the die face 26, thusmaintaining the process melt at a desired temperature in the extrusionorifice distal end 68, and to assist in creating a robust thermallyinsulated die plate assembly. While a trapezoidal cross-section for theraised circular ridge is preferred, other shapes for the ridgecross-section could be designed by those skilled in the art in order toachieve the foregoing goals, as contemplated by the present invention.

The assemblage as heretofore described encloses the circular recess 33to form the thin, continuous thermal air pocket or air chamber 32 whichis preferably connected to the surrounding atmosphere by at least onevent tube 44. Variation in temperature and/or pressure within the dieplate body 10 equilibrates by expansion or contraction of air into andthrough vent tube 44 thus avoiding vacuum formation and/or pressurebuild-up which could potentially lead to undesirable deformation of thedownstream face 26. Raised ridge 34 and orifice protrusions 35through-penetrate the atmospheric air pocket 32 to provide continuousand more uniform heating along the length of the through-penetratingextrusion orifices 22, and the weldment of their distal ends 70 to theopenings 39 in the cover plate 38 serve to strengthen and maintain theplanar shape of the cover plate.

As best seen in FIG. 2 the air pocket or chamber 32 is generallyparallel to the die face 26, but extends into the counterbore 76, as at78, in order to surround the outer periphery of each orifice protrusion35. The thickness of the air chamber 32 can vary at different locationsbut should be at least about 0.05 mm to no more than about 6.0 mm deep,and preferably is about 0.5 mm to about 1.0 mm deep. Stated another way,the thickness of the air chamber 32 in the dimension parallel to the dieface is preferably about 5% to about 10% of the thickness of the dieplate assembly 10.

Cover plate 38 preferably includes at least one circumferentialexpansion groove 62 on the portion of the cover plate 38 that extendsbeyond the circular array of extrusion orifices 22. More preferably, atleast one circumferential expansion groove 62 is on each side of coverplate 38 outside the array of extrusion orifices. Still more preferably,a multiplicity of circumferential expansion grooves 62 are positionedstaggeringly on opposite sides of the cover plate 38. Thecircumferential expansion grooves 62 can be of any geometry in profileincluding but not limited to square, angular, rounded, and hemisphericaland the multiplicity of grooves on cover plate 38 can be of similar ordiffering geometries. Preferably, the circumferential grooves arerounded in profile as shown in FIG. 2.

As described previously, the raised circular ridge 34 of the extrusionorifice extensions 31 is preferably unitary with die plate body 36 andtherefore of the same chemical composition.

The orifice protrusions 35, on the other hand, are formed as separatecollars and attachedly connected to the top of the raised ridge as bybrazing, welding, and any similar mechanism known to those skilled inthe art. The protrusions 35 can be of similar or differing compositionto the ridge 34 and die plate body 36 of which the composition caninclude but is not limited to tool steel, hardened tool steel, stainlesssteel, nickel steel, and the like.

Turning to FIGS. 4 through 9 there is shown a two-piece die plateassembly, generally designated by reference numeral 100, in accordancewith a second embodiment of the present invention. The die plateassembly 100 includes a die plate outer ring 105 and removable centerdie insert 106. Since many of the components of the die plate assembly100 are the same as or very similar to the components of the die plateassembly 10, the same reference numerals are carried forward from thelatter for corresponding components in the former, but preceded by the“1” digit.

Similarly to the FIG. 1 embodiment, the die plate assembly 100 isattachedly connected to an inlet housing 112 from a melting and/ormixing apparatus (not shown). The inlet housing 112 includes apassageway 114 for process melt as heretofore described. Nose cone 116directs the process melt to the upstream side 124 of the removableinsert 106 to which it is attachedly connected by threaded rod (notshown). The threaded rod is screw threaded at one end into threaded bore118 of nose cone 116 and at its distal end into threaded bore 120 ofremovable insert 106.

The removable center die insert 106 includes a multiplicity of extrusionorifices 122 concentrically arranged singly or in multiples thereof inat least one annular ring that extends from the upstream face 124 to thedownstream face 126 of removable insert 106. A plurality of knife bladeassemblies 128 mounted on a rotatably driven cutter hub 130 in a cuttingchamber (not shown) cut the extruded and at least partially solidifiedprocess melt into pellets. The pellets thusly formed are transportedmechanically, pneumatically, hydraulically, or in combinations thereofto downstream processing as before.

The central areas of the downstream face 126 of insert 106 are machinedor cut out to provide a central circular recess or cavity 133 in thesame manner as described above for the first embodiment, includingraised circular ridge 134 and orifice protrusions 135, which togetherdefine the extrusion orifice extensions 131 and encase the extrusionorifices 122 through the cavity 133. A circular cover plate 138 withholes 139 matching the distal ends 170 of the orifice protrusions 135overlays the recess cavity 133 to form a thin, continuous thermal airpocket or air chamber 132 across the insert 106 generally parallel tothe die face 126. The upstream side of cover plate 138 is also providedwith a generally circular counterbore 176 which includes the outletholes 139 and conforms to and receives the circular array of orificeprotrusions 135. The extrusion orifice extensions 131 made up of theraised circular ridge 134 and orifice protrusions 135 serve to channeland provide heat from the insert body 136 to the distal end 168 of theextrusion orifices 122, while at the same time the extensions 131 arethermally insulated from cover plate 138 by the air chamber 132 whichsurrounds the orifice extensions 131.

The cover plate 138 is attachedly connected to the periphery of theinsert body 136 and to orifice protrusion distal ends 170 by brazing,welding, or similar technique known to those skilled in the art.Preferably, the cover plate 138 is constructed of an abrasion andcorrosion resistant metal and more preferably is constructed of nickelsteel. Similarly, attachment of the cover plate 138 to the insert body136 and orifice protrusion distal ends 170 is preferably achieved bywelding and, more preferably, is achieved by nickel steel welding.Weldments 140 and 142 are preferentially made at circumferential grooves176 peripherally about the cover plate 138 and onto protrusion distalends 170 at weldment locus 142 (see FIG. 9). The surface of the coverplate 138 and thus the downstream face 126 of die insert 106 ispreferably coated with a chemical, abrasion, corrosion, and wearresistant coating as described hereinbelow.

The circular cavity 133 is preferably connected to the surroundingatmosphere by at least one vent tube 144 which passes through both theremovable die insert 106 and the die plate outer ring 105. Variation intemperature and/or pressure within the air chamber 132 equilibrates byexpansion or contraction of air into and through vent tube 144, thusavoiding vacuum formation and/or pressure build-up which couldpotentially lead to undesirable deformation of the downstream face 126.Raised ridge 134 and orifice protrusions 135 through-penetrate theatmospheric air pocket 132 to provide continuous and more uniformheating along the length of the extrusion orifices encompassedtherewithin. The configuration of the raised circular ridge 134,preferably trapezoidal in vertical cross-section, serves to channel heatto the orifice protrusions 135 in order to assist in maintaining theprocess melt in protrusions 135 at the desired temperature prior to exitfrom the distal end 168 of extrusion orifices 122. Weldment of theperiphery of the cover plate 138 to the insert 106 and of the distalends 170 of the orifice protrusions 135 in the holes 139 of the coverplate 138 serve to strengthen and rigidify the cover plate in its planarshape, as further described in the next paragraph.

The insert body 136 and cover plate 138 are designed with a multitude ofcomplementary abutting surfaces to improve the effectiveness of theweldments 140 and 142. This in turn increases the rigidity of theassembled cover plate 138 onto the insert body 136, improves the sealingof the air chamber 132 and provides an overall robust die plate assembly110. First, the machined cutout 133 includes peripheral ledge 182 (seeFIGS. 6 and 7) which receives a peripheral edge 184 of the cover plate138 to define the periphery of the air chamber 132. The complementaryabutting surfaces of the insert body peripheral ledge 182 and coverplate peripheral edge 184 are then held together by weldment 140.Second, holes 139 of cover plate 138 include a countersunk section 186on their upstream side (see FIG. 8) which forms a ledge 188 that engagesthe outer periphery of the distal ends 170 of the orifice protrusions135 (see FIG. 9). These complementary abutting surfaces 170 and 188 areadhered together by weldments 142 at each extrusion orifice 168.

The circular counterbore 176 in cover plate 138 differs from thecircular counterbore 76 in cover plate 38 in that the former iscontoured with tapered side walls 190 to more closely follow the contourof the tapered sides 192 of the raised ridge 134. By more closelyfollowing the contour of raised ridge 134, the counterbore 176 andresultant air chamber 132 provide additional insulation about the ridge134 and the associated orifice protrusions 135. In contrast, thecircular counterbore 76 is more rectangular in cross-section and ispositioned adjacent the raised ridge 34 without contouring dimensionallywith its tapered sides 92. It is understood that the contours of thecircular counterbore 176 adjacent raised circular ridge 134 and of thecounterbore 76 adjacent raised ridge 34 are only two non-limitingexamples and other designs comparable to and intermediate between thesetwo configurations are encompassed by the present invention. Use of therectangular counterbore 76 and tapered counterbore 176 can be applied tothe solid-body die plate assembly 10 as well as to the two-piece dieplate assembly 100.

If desired, cover plate 138 can be provided with circumferentialgrooves, such as grooves 62 illustrated and described above for coverplate 38.

Heating and/or cooling processes can be provided by electricalresistance, induction, steam or heat transfer fluid as has beenconventionally disclosed for the single-body die plate 10 as well as thetwo-piece die plate assembly 100. As shown in FIGS. 1 and 4, the dieplate body 36 and insert body 136 are each respectively heated by radialelectric heaters 46 and 146 positioned in radial slots 47 such as shownin FIG. 3, as well known in the art. In the two-piece die plate assembly100 shown in FIG. 4, the removable insert 106 and the die plate outerring 105 can each be separately heated by similar or differingmechanisms.

For example, FIG. 10 illustrates a partially exploded view of a dieplate assembly, generally designated by reference numeral 200, whichincludes a center-heated removable insert 208. Since many of thecomponents of the die plate assembly 200 are the same as or very similarto the components of the die plate assembly 100, the same referencenumerals are carried forward from the latter for correspondingcomponents in the former, but preceded by the “2” digit instead of the“1” digit.

The die plate assembly 200 thus includes a die plate body, generallydesignated by reference numeral 212, comprised of die plate outer ring205 surrounding center-heated removable insert 208. The electricalresistance coil 250 is contained in an annular recess or cavity 252centrally located within the insert 208 adjacent to the upstream face224. Nose cone 216 is attachedly connected to removable insert 208through use of a threaded rod (not shown) that is screw threaded at oneend into threaded bore 218 of nose cone 116 and at its distal end intothreaded bore 220 of removable insert 208 in a manner similar to thatshown in FIGS. 1 and 4. When attached, nose cone 116 closes off cavity252 with coil 250 positioned therein. Other methods of fastening arewell-known to those skilled in the art. The removable insert 208 canthus be heated separately as by electric radial heaters 146 hereinbeforedescribed in connection with the die plate assembly 100 shown in FIG. 4.

The downstream face 26, 126 of die plate assembly 10, 100, 200 can be inone plane as shown in FIG. 1 but preferably is of two parallel planes asindicated by the encircled area 66, 166 in FIGS. 2 and 9, wherein thearea adjacent to the outlets 68, 168 of extrusion orifices 22, 122 israised in a plane parallel to that of the downstream face 26, 126. Theelevation of the plane above that of the downstream face 26 should be atleast approximately 0.025 mm, and preferably is at least approximately0.50 mm.

Similarly, the recess cavity 33, 133 is at least approximately 1.05millimeters in depth, preferably on the order of 5.0 mm to 7.0 mm. Thethickness of the cover plate 38, 138 should be on the order of 1.0 mm to8.0 mm, preferably about 6.0 mm in order to provide a thickness of theair chamber 32, 132 on the order of about 0.05 mm to about 6.0 mm, andpreferably about 0.5 mm to about 1.0 mm.

The surface of the downstream face 26, 126 is preferably subjected to achemical, abrasion, corrosion, and/or wear resistant treatment, i.e.,“surface treatment,” in the annular area generally defined by the arrayof extrusion orifice outlets 68, 168 and identified by the numeral 60,160 in FIGS. 2 and 9. This annular area includes the cutting face 63,163 where the cutting blades engage the die face. The surface treatmentshould be at least approximately 0.025 mm, and preferably is at leastapproximately 0.50 mm. The composition of the surface treatment 60, 160can be different in the planar area surrounding the extrusion orificeoutlets 68, 168 than that on other parts of the downstream face 26.Preferably, the surface treatment 60, 160 is the same on all faces andcan involve one, two, or a multiplicity of processes inclusive andexemplary of which are cleaning, degreasing, etching, primer coating,roughening, grit-blasting, sand-blasting, peening, pickling, acid-wash,base-wash, nitriding, carbonitriding, electroplating, electrolessplating, electroless nickel dispersion treatments, flame sprayingincluding high velocity applications, thermal spraying, plasmatreatment, electrolytic plasma treatments, sintering, powder coating,vacuum deposition, chemical vapor deposition, physical vapor deposition,sputtering techniques, spray coating, and vacuum brazing of carbides.

Surface treatment for all surfaces, other than the cutting face,includes flame spray, thermal spray, plasma treatment, electrolessnickel dispersion treatments, high velocity air and fuel modifiedthermal treatments, and electrolytic plasma treatments, singly and incombinations thereof. These surface treatments metallize the surface,preferably fixedly attach metal nitrides to the surface, more preferablyfixedly attach metal carbides and metal carbonitrides to the surface,and even more preferably fixedly attach diamond-like carbon to thesurface, still more preferably attach diamond-like carbon in anabrasion-resistant metal matrix to the surface, and most preferablyattach diamond-like carbon in a metal carbide matrix to the surface.Other ceramic materials can be used and are included herein by way ofreference without intending to be limiting. These preferred surfacetreatments can be further modified optionally by application ofconventional polymeric coating on the downstream face 26, 126 distalfrom the extrusion orifice outlet 68, 168. The polymeric coatings arethemselves non-adhesive and of low coefficient of friction. Preferablythe polymeric coatings are silicones, fluoropolymers, and combinationsthereof. More preferably the application of the polymeric coatingsrequires minimal to no heating to effect drying and/or cure.

FIG. 11 illustrates additional configurations of extrusion orifices andorifice protrusions projecting from the raised circular ridge. FIG. 11 aillustrates concentric rings of orifice protrusions 302 projecting fromridge 303 in staggered formation, each protrusion having a singleextrusion orifice 304. The extrusion orifices can be oriented in amultiplicity of groups or pods 306 as illustrated in FIG. 11 b for agrouping of two extrusion orifices 308, FIG. 11 c for a grouping ofthree extrusion orifices 310, FIG. 11 d for a cluster of four extrusionorifices 312, FIG. 11 e for a pod of sixteen extrusion orifices 314,FIG. 11 f for a multiplicity of thirty-seven extrusion orifices 316, andFIG. 11 g for a multiplicity of sixteen extrusion orifices 318.

Groups, clusters, pods, and a multiplicity thereof can be arranged inany geometric configuration including but not limited to oval, round,square, triangular, rectangular, polygonal, and combinations thereof.The geometries of the orifice protrusions can be further rounded,angled, and chamfered and can contain any number of a multiplicity oforifices. Orientation of the geometries containing the multiplicity oforifices can be circumferentially and parallel to the arc,circumferentially and perpendicular to the arc, staggered andalternatingly circumscribing the arc and any combination thereof.Furthermore, the geometric orientation may conform to the arc as in akidney shape or comma-shape. A multiplicity of concentric rings, atleast one or more, of extrusion orifices can include extrusion orifices,singly or a multiplicity thereof, that can be arranged in a lineararray, alternatingly, staggeredly, and any combination thereof relativeto the other concentric rings in accordance with the instant invention.

Further, while the outlet of the extrusion orifices 22, 122, such asoutlet 68 in FIG. 2 and outlet 168 in FIG. 9, is preferably round, theoutlets can be of any geometry including but not limited to round, oval,square, rectangular, triangular, pentagonal, hexagonal, polygonal,slotted, radially slotted and any combination thereof. A multiplicity ofextrusion orifice outlets 68 can be of different geometry in aparticular protrusion 35.

Further, the extrusion orifice extensions may include more than oneraised circular ridge 34, 134, depending upon the arrangement of theextrusion orifices and the width of the cutting blade. In addition,although at least one raised circular ridge 34, 134 is preferred to formthe base of the extrusion orifice extensions 31, 131, it may be possibleto design the extensions 31, 131 without any raised ridge. In suchcircumstances, the orifice protrusions 35, 135 would extend from thebase of cutout 33, 133 to the respective opening 68, 168 of the coverplate 38, 138.

The foregoing is considered as illustrative only of the principles ofthe invention. Numerous modifications and changes will readily occur tothose skilled in the art. Therefore, it is not desired to limit theinvention to the exact construction and operation shown and described,and, accordingly, all suitable modifications and equivalents may beresorted to, falling within the scope of the invention.

1-19. (canceled)
 20. A thermally insulated extrusion die plate assemblyfor a pelletizer including a plurality of extrusion orifices throughwhich process melt is extruded to exit at a cutting face as a strand tobe cut into pellets by a moving cutting assembly which comprises: a dieplate body having a downstream face, a portion of said downstream facebeing cut out to form a recess or cavity in said downstream face; saidextrusion orifices having a plurality of extrusion orifice extensionsthat extend through said cavity; and a cover plate attached to said dieplate body to form said cutting face, said cover plate fitted over andenclosing said cavity to form and define a thermally insulating airchamber in said assembly adjacent said cutting face, said orificeextensions through-penetrating said air chamber and said cover platehaving openings therethrough which mate with said extrusion orificesextensions, said air chamber surrounding and insulating said orificeextensions to prevent heat loss from the process melt adjacent thecutting face.
 21. The assembly as claimed in claim 20, wherein the dieplate body is a single-body construction that is thermally regulated byat least one of electrical resistance, induction, steam, and thermaltransfer fluid.
 22. The assembly as claimed in claim 20, wherein the dieplate body is a two-piece construction including a removable insert anda die plate outer ring that are thermally regulated by at least one ofelectrical resistance, induction, steam, or thermal transfer fluid. 23.The assembly as claimed in claim 20, wherein said cover plate has acounter-bore which conforms to a shape of said extrusion orificeextensions to further define said thermally insulating air pocket. 24.The assembly as claimed in claim 23, wherein said extrusion orificeextensions are configured as a raised circular ridge continuous andunitary with said die plate body, and individual orifice protrusionsextend from said raised ridge to said cover plate.
 25. The assembly asclaimed in claim 24, wherein said raised circular ridge is configured tochannel heat to said orifice protrusions.
 26. The assembly as claimed inclaim 24, wherein said cover plate counter-bore is sized so that thethermally insulating air chamber follows the contour of the raisedcircular ridge.
 27. The assembly as claimed in claim 24, wherein theorifice protrusions are separate elements attachedly connected to theraised circular ridge on the die plate body.
 28. A thermally insulatedextrusion die plate assembly for a pelletizer including a plurality ofextrusion orifices through which process melt is extruded to exit at acutting face as a strand to be cut into pellets by a moving cuttingassembly which comprises: a die plate body having a downstream face; acover plate attached to the downstream face to form said cutting face; athermally insulating air chamber formed between said downstream face andsaid cover plate upon attachment of said cover plate to said die platebody; and a plurality of extrusion orifice extensionsthrough-penetrating said air chamber and said die plate body, saidextrusion orifice extensions being surrounded and insulated by said airchamber to provide continuous and more uniform heating along a length ofsaid extrusion orifice extensions.
 29. The assembly as claimed in claim28, wherein said air chamber is in direct communication with asurrounding atmosphere outside the die plate assembly to keep air insaid chamber at atmospheric pressure.
 30. The assembly as claimed inclaim 29, wherein a portion of said downstream face of the die platebody is cut out to form a recess or cavity, said air chamber beingformed and defined by said cavity and said cover plate attached to thedownstream face.
 31. The assembly as claimed in claim 30, wherein saidextrusion orifice extensions are configured as a raised circular ridgecontinuous and unitary with said die plate body, said raised circularridge being configured to channel heat to said orifice protrusions andsaid cover plate having a counter-bore which conforms to a shape of saidextrusion orifice extensions and is sized so that the thermallyinsulating chamber follows the contour of the raised circular ridge. 32.The assembly as claimed in claim 28, wherein said assembly includes avent configured to equilibriatingly vent said thermally insulatingchamber to an ambient atmosphere outside of said die plate assembly toprevent pressure build up and/or vacuum formation in said air chamber.33. The assembly as claimed in claim 20 in combination with anunderfluid pelletizer.
 34. The assembly as claimed in claim 28, whereinsaid air chamber extends between and on either side of the extrusionorifice extensions, said extrusion orifice extensions dividing the airchamber into an outer section and an inner section.
 35. An underwaterpelletizer for extruding and cutting a process melt into pelletscomprising: a die plate body with a plurality of extrusion orificesformed therein through which the process melt is carried from said dieplate body to a cutting face on a downstream side of said die platebody; a rotary cutter blade assembly in opposed relation to said cuttingface, said cutter blade assembly having a hub and at least one cutterblade mounted on said hub and capable of moving in a plane generallyparallel to and closely adjacent said cutting face to cut strands ofprocess melt extruded through said orifices into pellets; a water boxhaving a cutting chamber enclosing said cutting face and cutter bladeassembly, said water box including a water inlet for introducing coolingwater into the cutting chamber and an outlet for discharge of water andpellets entrained in the water; a die plate body having a downstreamface; a cover plate attached to the downstream face to form said cuttingface; a thermally insulating air chamber formed between said downstreamface and said cover plate upon attachment of said cover plate to saiddie plate body; a plurality of extrusion orifice extensionsthrough-penetrating said air chamber and being surrounded and insulatedby said air chamber to provide continuous and more uniform heating alonga length of said extrusion orifice extensions, said cover plate havingopenings therethrough which mate with said extrusion orificesextensions, distal ends of said extrusion orifice extensions beingattachedly connected to said cover plate adjacent said cover plateopenings.
 36. The underwater pelletizer as claimed in claim 35, whereina portion of said downstream face of the die plate body is cut out toform a recess or cavity, said air chamber being formed and defined bysaid cavity and said cover plate attached to the downstream face. 37.The underwater pelletizer as claimed in claim 36, wherein said extrusionorifice extensions are configured as a raised circular ridge continuousand unitary with said die plate body and individual orifice protrusionsextending from said raised ridge, distal ends of said orificeprotrusions being attachedly connected to said cover plate.
 38. Theunderwater pelletizer as claimed in claim 37, wherein said cover platehas a counter-bore which conforms to a shape of said extrusion orificeextensions and is sized so that the thermally insulating air chamberfollows a contour of the raised circular ridge, said raised circularridge dividing said air chamber into a generally annular outer sectionand a generally circular inner section.
 39. The underwater pelletizer asclaimed in claim 35, further comprising radial electric heaterspositioned in radial slots in said die plate body, said die plate bodychanneling heat from said heaters to said extrusion orifice extensions.40. The underwater pelletizer as claimed in claim 35, wherein said airchamber is vented to an atmosphere outside the die plate assembly toprevent pressure build up and/or vacuum formation in said air chamber.41. The assembly as claimed in claim 28, wherein said thermallyinsulating air chamber is equilibriatingly vented to atmosphere outsideof the die plate assembly.
 42. The assembly as claimed in claim 28,wherein said cutting face has a surface treatment applied thereto thatincludes at least one of nitriding, carbonitriding, electroplating,electroless plating, electroless nickel dispersion treatments, flamespraying including high velocity applications, thermal spraying, plasmatreatment, electrolytic plasma treatments, sintering, powder coating,vacuum deposition, chemical vapor deposition, physical vapor deposition,sputtering techniques, spray coating, and vacuum brazing of carbides.43. The assembly as claimed in claim 28, wherein an outside surface ofsaid cover plate including said cutting face has at least one chemical,corrosion, abrasion or wear-resistant surface treatment applied thereto.44. The assembly as claimed in claim 28, wherein said plurality ofextrusion orifice extensions are configured as a raised circular ridgecontinuous and unitary with said die plate body and individual orificeprotrusions extending from said raised ridge to said cover plate, saidorifice protrusions being through-penetrated by a multiplicity ofextrusion orifices that are arranged in at least one of groups, pods,and clusters.
 45. The assembly as claimed in claim 44, wherein theorifice protrusions have at least one geometry selected from the groupconsisting of oval, round, square, triangular, polygonal, andcombinations thereof; said orifice protrusions have an arrangementselected from the group consisting of concentrically alternating,staggeredly, linearly, and combinations thereof; said orificeprotrusions are parallel to the arc of the cutting face or perpendicularto the arc; and said orifice protrusions have a kidney- to comma-shapedconfiguration.
 46. The assembly as claimed in claim 44, wherein saidcover plate has openings therein which mate with said extrusionorifices, said cover plate being attached to distal ends of said orificeprotrusions at the openings in said cover plate.
 47. The assembly asclaimed in claim 28, wherein said cover plate contains a multiplicity ofcircumferential expansion grooves on both faces in a staggered andalternating configuration.
 48. The assembly as claimed in claim 28,wherein said cover plate is made of nickel steel and is weldinglyattached by nickel steel.
 49. The assembly as claimed in claim 28,wherein outlets of said extrusion orifice extensions at said cuttingface have a geometry selected from the group consisting of round, oval,square, rectangular, triangular, pentagonal, hexagonal, polygonal,slotted, radially slotted and any combination thereof.